Delivery of CRT therapy during AT/AF termination

ABSTRACT

In some embodiments, a method for operating a cardiac rhythm management device may include one or more of the following steps: (a) sensing atrial depolarizations through an implanted atrial electrode, (b) administering a sequential CRT pacing therapy in a sequential CRT pacing mode to a left and right ventricle of a heart of a patient via implanted ventricular electrodes in a sequential bi-ventricular fashion, (c) switching from the sequential CRT pacing mode to a simultaneous CRT pacing mode, (d) administering a simultaneous CRT pacing therapy in the simultaneous CRT pacing mode to the left and right ventricle in a simultaneous bi-ventricular fashion, (e) analyzing the sensed atrial depolarizations to detect the presence of an atrial arrhythmia, (f) analyzing the sensed atrial depolarizations while in the sequential CRT pacing mode to detect the presence of atrial arrhythmia, and (g) sensing ventricular depolarizations of the left and the right ventricle.

FIELD

The disclosure generally pertains to embodiments for cardiac rhythmmanagement. In particular, some embodiments relate to methods andapparatuses for providing cardiac resynchronization therapy (CRT) alongwith atrial therapies such as cardioversion and anti-tachy pacing.

BACKGROUND SECTION

In the context of dual chamber pacing, a variety of mode switchingfeatures have been developed which detect an excessively rapid atrialrhythm and, in response, cause the pacemaker to switch from an atrialsynchronized pacing mode, such as DDD, to a non-synchronized mode suchas VVI or DDI. Such mode switching features are disclosed in U.S. Pat.No. 5,144,949, by Olson, U.S. Pat. No. 5,318,594, by Limousin et al.,U.S. Pat. No. 4,944,298, by Sholder, U.S. Pat. No. 5,292,340, by Crosbyet al. and U.S. Pat. No. 4,932,406 by Berkovits, all incorporated hereinby reference in their entireties. In such devices, the primary purposeof the mode switch is to prevent the pacemaker from tracking anon-physiologic atrial rate.

It is common in dual chamber pacing with both atrial and ventricularsensing leads for the atrial sensing channel to be blanked after aventricular event for a specified blanking interval. This is done toavoid oversensing, including far-field sensing of ventriculardepolarizations by the atrial sensing lead. The blanking periods cancomplicate the detection of atrial tachycardia or atrial flutter sincethe blanking periods can block detection of some atrial events. Further,a dual chamber device with pacing pulse timing optimized to improvepatient hemodynamics may have sequential right and left ventricularpacing pulses that are often separated in time by as much as 80 ms. Thesequential pacing of such devices increases the atrial blanking periodand, thereby, increases the difficulty of detecting AF or atrialflutter.

BRIEF SUMMARY OF THE INVENTION

The present invention is an implantable medical device (IMD) thatprovides cardiac resynchronization therapy (CRT). Sequential andsimultaneous CRT including atrial pacing are selectively implanted basedon continuous monitoring cardiac rhythm to detect arrhythmias.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram illustrating an exemplary implantablemedical device implanted in a patient that selectively switches toatrial pacing or defibrillation during delivery of pacing pulsesaccording to sensed atrial abnormalities.

FIG. 2 is conceptual diagram further illustrating the implantablemedical device of FIG. 1 and the heart of the patient.

FIG. 3 shows a functional schematic diagram of an implantablepacemaker/cardioverter/defibrillator within which certain embodiments ofthe invention may be practiced.

FIGS. 4-6 are marker channel diagrams for simultaneous pacing of bothventricles or single pacing of one ventricle in certain embodiments ofthe present invention.

FIG. 7A shows a marker channel diagram for sequential pacing of bothventricles in certain embodiments of the present invention.

FIG. 7B shows a marker channel diagram for simultaneous or singleventricle pacing in certain embodiments of the present invention.

FIG. 7C shows a marker channel diagram for a blanking period during anatural depolarization event in certain embodiments of the presentinvention.

FIG. 8 shows a flow chart diagram of an atrial arrhythmia detectionmethod according to certain embodiments of the present invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The following discussion is presented to enable a person skilled in theart to make and use the present invention. Various modifications to theillustrated embodiments will be readily apparent to those skilled in theart, and the generic principles herein may be applied to otherembodiments and applications without departing from the presentinvention. Thus, the present invention is not intended to be limited toembodiments shown, but is to be accorded the widest scope consistentwith the principles and features disclosed herein. The followingdetailed description is to be read with reference to the figures, inwhich like elements in different figures have like reference numerals.The figures, which are not necessarily to scale, depict selectedembodiments and are not intended to limit the scope of the claimedinvention. Skilled artisans will recognize the examples provided hereinhave many useful alternatives and fall within the scope of the presentinvention.

With reference to FIG. 1, a conceptual diagram illustrating an exemplaryimplantable medical device implanted in a patient that selectivelyprovides atrial pacing or defibrillation along with the delivery of aCRT therapy according to sensed atrial abnormalities is shown.

According to certain embodiments of the invention, IMD 10 selectivelyprovides right atrial delivery of pacing pulses or defibrillation pulsesduring periods of bi-ventricular pacing based on an algorithm in orderto eliminate atrial arrhythmias and improve the hemodynamic performanceof the heart 16 of patient 12. IMD 10, as shown in FIG. 1, takes theform of a pacemaker or defibrillator providing a CRT therapy.

IMD 10 includes leads 14A, 14B, and 14C (collectively “leads 14”) thatextend into heart 16. More particularly, right ventricular (RV) lead 14Aextends through one or more veins (not shown), the superior vena cava(not shown), and right atrium 24, and into right ventricle 18. Leftventricular (LV) coronary sinus lead 14B extends through the veins, thevena cava, right atrium 24, and into the coronary sinus 20 to a pointadjacent to the free wall of left ventricle 22 of heart 16. Right atrial(RA) lead 14C extends through the veins and vena cava, and into theright atrium 24 of heart 16.

IMD 10 senses electrical signals attendant to the depolarization andrepolarization of heart 16, and provides pacing pulses via electrodes(not shown) located on leads 14. IMD 10 can also provide cardioversionor defibrillation pulses via electrodes located on leads 14. Thesense/pace electrodes located on leads 14 may be unipolar or bipolar, asis well known in the art.

During periods of possible atrial fibrillation or tachycardia, IMD 10can deliver simultaneous bi-ventricular pacing pulses or suspend thebi-ventricular pacing according to an algorithm to stabilize the atrialrate. As will be described in greater detail below, IMD 10 can receive asignal, e.g., an electrogram that represents electrical activity withinheart 16, and process the signal to detect abnormalities in atrium 24.In response, IMD 10 can synchronize or suspend the sequentialbi-ventricular pacing to reduce any “blanking” periods. With a reducedblanking period, IMD 10 can sense signals in the atrium 24 over agreater percentage of a heart cycle, thus allowing IMD 10 to betterdetermine if an atrial abnormality is occurring. Blanking periods areused to prevent saturation of the sense amplifier or to preventoversensing. The sensing electrode can be blanked for a specifiedblanking interval by disabling the sense amplifier when a pace isdelivered.

The configuration of IMD 10 and leads 14 illustrated in FIG. 1 is merelyexemplary. IMD 10 may be coupled any number of leads 14 that extend to avariety of positions within or outside of heart 16. For example, atleast some of leads 14 may be epicardial leads. Further, IMD 10 need notbe implanted within patient 12, but may instead be coupled withsubcutaneous leads 14 that extend through the skin of patient 12 to avariety of positions within or outside of heart 16.

With reference to FIG. 2, conceptual diagram further illustrating theimplantable medical device of FIG. 1 and the heart of the patient isshown. Each of leads 14 includes an elongated insulative lead bodycarrying a number of concentric coiled conductors separated from oneanother by tubular insulative sheaths. Located adjacent distal end ofleads 14A, 14B, and 14C are bipolar electrodes 30 and 32, 34 and 36, and38 and 40 respectively. Electrodes 30, 34, and 38 may take the form ofring electrodes, and electrodes 32, 36, and 40 may take the form ofextendable helix tip electrodes mounted retractably within insulativeelectrode heads 42, 44, and 46, respectively. Each of the electrodes30-40 is coupled to one of the coiled conductors within the lead body ofits associated lead 14.

Sense/pace electrodes 30, 32, 34, 36, 38, and 40 sense electricalsignals attendant to the depolarization and repolarization of heart 16.The electrical signals are conducted to IMD 10 via leads 14. Sense/paceelectrodes 30, 32, 34, 36, 38 and 40 further deliver pacing pulses tocause depolarization of cardiac tissue in the vicinity thereof. IMD 10may also include one or more housing electrodes, such as housingelectrode 48, formed integral with an outer surface of the hermeticallysealed housing 50 of IMD 10. Any of electrodes 30, 32, 34, 36, 38, and40 may be used for unipolar sensing or pacing in combination withhousing electrode 48.

The invention is not limited to the sense/pace electrode locationsillustrated in FIG. 2. For example, in the example embodimentillustrated in FIG. 2, tip electrode 32 of RV lead 14A is disposed inthe apical region of right ventricle 18. However, in other embodiments,tip electrode 32 may be located near the pulmonary artery outflow tract(not shown) or the bundle of His. Such alternative locations may provideimproved response or conduction, and thus hemodynamically beneficial,contraction of ventricles 18 and 22 through delivery of pacing at asingle location by delivering pulses near the specialized conductionsystem of heart 16.

Leads 14A, 14B and 14C may also, as shown in FIG. 2, include elongatedcoil electrodes 52, 54 and 56, respectively. IMD 10 may deliverdefibrillation or cardioversion shocks to heart 16 via defibrillationelectrodes 52-56. Defibrillation electrodes 52-56 may be fabricated fromplatinum, platinum alloy or other materials known to be usable inimplantable defibrillation electrodes, and can be about 5 cm in length.

With reference to FIG. 3, a functional schematic diagram of animplantable medical device in which certain embodiments of the inventionmay be practiced is shown. This diagram should be taken as exemplary ofthe type of device in which certain embodiments of the invention may beembodied, and not as limiting, as it is believed that the invention mayusefully be practiced in a wide variety of device implementations,including devices such as cardioverters and defibrillators which do notprovide anti-tachycardia pacing therapies, anti-tachycardia pacemakerswhich do not provide cardioversion or defibrillation, and devices whichdeliver different forms of anti-arrhythmia therapies such nervestimulation or drug administration.

The device is provided with a lead system including electrodes, whichmay be as illustrated in FIG. 2. Alternate lead systems may of course besubstituted. If the electrode configuration of FIG. 2 is employed, thecorrespondence to the illustrated electrodes is as follows.

Electrode 311 corresponds to housing electrode 48, and is thenon-insulated portion of the housing of the implantable device.Electrode 320 corresponds to electrode 52 and is a defibrillationelectrode located in the right ventricle. Electrode 310 corresponds toelectrode 54 and is a defibrillation electrode located in the coronarysinus. Electrode 318 corresponds to electrode 42 and is a defibrillationelectrode located in the superior vena cava. Electrodes 324 and 326correspond to electrodes 30 and 32, and are used for sensing and pacingin the ventricle. Electrodes 317 and 321 correspond to electrodes 46 and38 and are used for pacing and sensing in the atrium.

Electrodes 310, 311, 318, and 320 are coupled to high voltage outputcircuit 234. Electrodes 324 and 326 are coupled to the R-wave amplifier200, which preferably takes the form of an automatic gain controlledamplifier providing an adjustable sensing threshold as a function of themeasured R-wave amplitude. A signal is generated on R-out line 202whenever the signal sensed between electrodes 324 and 326 exceeds thepresent sensing threshold.

Electrodes 317 and 321 are coupled to the P-wave amplifier 204, whichmay also take the form of an automatic gain controlled amplifierproviding an adjustable sensing threshold as a function of the measuredR-wave amplitude. A signal is generated on P-out line 206 whenever thesignal sensed between electrodes 317 and 321 exceeds the present sensingthreshold. The general operation of the R-wave and P-wave amplifiers 200and 204 may correspond to that disclosed in U.S. Pat. No. 5,117,824, byKeimel, et al., issued Jun. 2, 1992, for an Apparatus for MonitoringElectrical Physiologic Signals, incorporated herein by reference in itsentirety.

Switch matrix 208 is used to select which of the available electrodesare coupled to wide band (0.5-200 Hz) amplifier 210 for use in digitalsignal analysis. Selection of electrodes is controlled by the controlleror microprocessor 224 via data/address bus 218, which selections may bevaried as desired. Signals from the electrodes selected for coupling tobandpass amplifier 210 are provided to multiplexer 220, and thereafterconverted to multi-bit digital signals by A/D converter 222, for storagein random access memory 226 under control of direct memory accesscircuit 228. Microprocessor 224 may employ digital signal analysistechniques to characterize the digitized signals stored in random accessmemory 226 to recognize and classify the patient's heart rhythmemploying any of the numerous signal-processing methodologies known tothe art.

The remainder of the circuitry is dedicated to the provision of cardiacpacing, cardioversion and defibrillation therapies, and, for purposes ofthe present disclosure may correspond to circuitry known in the priorart. An exemplary apparatus is disclosed for accomplishing pacing,cardioversion, and defibrillation functions as follows. The pacertiming/control circuitry 212 includes programmable digital counterswhich control the basic time intervals associated with DDD, VVI, DVI,VDD, AAI, DDI and other modes of single and dual chamber pacing wellknown to the art. Circuitry 212 also controls escape intervalsassociated with anti-tachyarrhythmia pacing in both the atrium and theventricle, employing, any anti-tachyarrhythmia pacing therapies known tothe art.

Intervals defined by pacing circuitry 212 include atrial and ventricularpacing escape intervals, the refractory periods during which sensedP-waves and R-waves are ineffective to restart timing of the escapeintervals and the pulse widths of the pacing pulses. The durations ofthese intervals are determined by microprocessor 224, in response tostored data in memory 226 and are communicated to the pacing circuitry212 via address/data bus 218. Pacer circuitry 212 also determines theamplitude of the cardiac pacing pulses under control of microprocessor224.

During pacing, the escape interval counters within pacer timing/controlcircuitry 212 are reset upon sensing of R-waves and P-waves as indicatedby signals on lines 202 and 206, and in accordance with the selectedmode of pacing on time-out trigger generation of pacing pulses by paceroutput circuits 214 and 216, which are coupled to electrodes 317, 321,324 and 326. The escape interval counters are also reset on generationof pacing pulses, and thereby control the basic timing of cardiac pacingfunctions, including anti-tachyarrhythmia pacing.

The durations of the intervals defined by the escape interval timers aredetermined by microprocessor 224, via data/address bus 218. The value ofthe count present in the escape interval counters when reset by sensedR-waves and P-waves may be used to measure the durations of R-Rintervals, P-P intervals, P-R intervals and R-P intervals, whichmeasurements are stored in memory 226 and used in conjunction withcertain embodiments of the present invention to diagnose the occurrenceof a variety of tachyarrhythmias, as discussed in more detail below.

Microprocessor 224 operates as an interrupt driven device, and isresponsive to interrupts from pacer timing/control circuitry 212corresponding to the occurrences of sensed P-waves and R-waves andcorresponding to the generation of cardiac pacing pulses. Theseinterrupts are provided via data/address bus 218. Any necessarymathematical calculations to be performed by microprocessor 224 and anyupdating of the values or intervals controlled by pacer timing/controlcircuitry 212 take place following such interrupts. Microprocessor 224includes associated ROM in which the stored program controlling itsoperation as described below resides. A portion of the memory 226 may beconfigured as a plurality of recirculating buffers, capable of holdingseries of measured intervals, which may be analyzed in response to theoccurrence of a pace or sense interrupt to determine whether thepatient's heart is presently exhibiting atrial or ventriculartachyarrhythmia.

The arrhythmia detection method of certain embodiments of the presentinvention can include prior art tachyarrhythmia detection algorithms. Asdescribed below, the entire ventricular arrhythmia detection methodologyof presently available Medtronic pacemaker/cardioverter/defibrillatorsis employed as part of the arrhythmia detection and classificationmethod according to certain embodiments of the present invention.However, any of the various arrhythmia detection methodologies known tothe art might also usefully be employed in alternative embodiments ofthe present invention.

In the event that an atrial or ventricular tachyarrhythmia is detected,and an anti-tachyarrhythmia pacing regimen is desired, appropriatetiming intervals for controlling generation of anti-tachyarrhythmiapacing therapies are loaded from microprocessor 224 into the pacertiming and control circuitry 212, to control the operation of the escapeinterval counters therein and to define refractory periods during whichdetection of R-waves and P-waves is ineffective to restart the escapeinterval counters. Alternatively, circuitry for controlling the timingand generation of anti-tachycardia pacing pulses as described in U.S.Pat. No. 4,577,633, issued to Berkovits al. on Mar. 25, 1986, U.S. Pat.No. 4,880,005, issued to Pless al. on Nov. 14, 1989, U.S. Pat. No.7,726,380, issued to Vollmann al. on Feb. 23, 1988 and U.S. Pat. No.4,587,970, issued to Holley al. on May 13, 1986, all of which areincorporated herein by reference in their entireties may also be used.

In the event that generation of a cardioversion or defibrillation pulseis required, microprocessor 224 employs the escape interval counter tocontrol timing of such cardioversion and defibrillation pulses, as wellas associated refractory periods. In response to the detection of atrialrequiring a cardioversion pulse, microprocessor 224 activatescardioversion/defibrillation control circuitry 230, which initiatescharging of the high voltage capacitors 246, 248 via charging circuit236, under control of high voltage charging control line 240. Thevoltage on the high voltage capacitors is monitored via VCAP line 244,which is passed through multiplexer 220 and in response to reaching apredetermined value set by microprocessor 224, results in generation ofa logic signal on Cap Full (CF) line 254, terminating charging.Thereafter, timing of the delivery of the defibrillation orcardioversion pulse is controlled by pacer timing/control circuitry 212.Following delivery of the fibrillation or tachycardia therapy themicroprocessor then returns the device to cardiac pacing and awaits thenext successive interrupt due to pacing or the occurrence of a sensedatrial or ventricular depolarization.

One embodiment of an appropriate system for delivery and synchronizationof ventricular cardioversion and defibrillation pulses and forcontrolling the timing functions related to them is disclosed in moredetail in commonly assigned U.S. Pat. No. 5,188,105 by Keimel, issuedFeb. 23, 1993, and incorporated herein by reference in its entirety.Appropriate systems for delivery and synchronization of atrialcardioversion and defibrillation pulses and for controlling the timingfunctions related to them may be found in PCT Patent Application No.W092/18198 by Adams et al., published Oct. 29,1992, and in U.S. Pat. No.4,316,472 by Mirowski et al., issued Feb. 23, 1982, both incorporatedherein by reference in their entireties. In addition, high frequencypulse bursts may be delivered to electrodes 317 and 321 to terminateatrial tachyarrhythmias, as described in PCT Patent Publication No.W095/28987, filed by Duffin et al. and PCT Patent Publication No.W095/28988, filed by Mehra et al, both incorporated herein by referencein their entireties.

However, any known cardioversion or defibrillation pulse controlcircuitry is believed usable in conjunction with certain embodiments ofthe present invention. For example, circuitry controlling the timing andgeneration of cardioversion and defibrillation pulses as disclosed inU.S. Pat. No. 4,384,585, issued to Zipes on May 24, 1983, in U.S. Pat.No. 4,949,719 issued to Pless et al, cited above, and in U.S. Pat. No.4,375,817, issued to Engle et al, all incorporated herein by referencein their entireties may also be employed.

In the illustrated device, delivery of the cardioversion ordefibrillation pulses is accomplished by output circuit 234, undercontrol of control circuitry 230 via control bus 238. Output circuit 234determines whether a monophasic or biphasic pulse is delivered, whetherthe housing 311 serves as cathode or anode and which electrodes areinvolved in delivery of the pulse. An example of output circuitry fordelivery of biphasic pulse regimens may be found in the above citedpatent issued to Mehra and in U.S. Pat. No. 4,727,877, incorporated byreference in its entirety.

An example of circuitry, which may be used to control delivery ofmonophasic pulses, is set forth in commonly assigned U.S. Pat. No.5,163,427, by Keimel, issued Nov. 17,1992, also incorporated herein byreference in its entirety. However, output control circuitry asdisclosed in U.S. Pat. No. 4,953,551, issued to Mehra et al. on Sep. 4,1990 or U.S. Pat. No. 4,800,883, issued to Winstrom on Jan. 31, 1989both incorporated herein by reference in their entireties, may also beused in conjunction with a certain embodiments of the present inventionfor delivery of biphasic pulses.

In modern implantable cardioverter/defibrillators, the physicianprograms the particular therapies into the device ahead of time, and amenu of therapies is typically provided. For example, on initialdetection of an atrial tachycardia, an anti-tachycardia pacing therapymay be selected and delivered to the chamber in which the tachycardia isdiagnosed or to both chambers. On redetection of tachycardia, a moreaggressive anti-tachycardia pacing therapy may be scheduled. If repeatedattempts at anti-tachycardia pacing therapies fail, a higher-levelcardioversion pulse may be selected thereafter. Therapies fortachycardia termination may also vary with the rate of the detectedtachycardia, with the therapies increasing in aggressiveness as the rateof the detected tachycardia increases. For example, fewer attempts atanti-tachycardia pacing may be undertaken prior to delivery ofcardioversion pulses if the rate of the detected tachycardia is above apreset threshold. The references cited above in conjunction withdescriptions of prior art tachycardia detection and treatment therapiesare applicable here as well.

In the event that fibrillation is identified, high frequency burststimulation as discussed above may be employed as the initial attemptedtherapy. Subsequent therapies may be delivery of high amplitudedefibrillation pulses, typically in excess of 5 joules. Lower energylevels may be employed for cardioversion. As in the case of currentlyavailable implantable pacemakers/cardioverter/defibrillators, and asdiscussed in the above-cited references, it is envisioned that theamplitude of the defibrillation pulse may be incremented in response tofailure of an initial pulse or pulses to terminate fibrillation. Priorart patents illustrating such pre-set therapy menus ofanti-tachyarrhythmia therapies include the above-cited U.S. Pat. No.4,830,006, issued to Haluska, et al., U.S. Pat. No. 4,727,380, issued toVollmann et al. and U.S. Pat. No. 4,587,970, issued to Holley et al.

Currently available implantable cardiac rhythm management devices,including bradycardia and tachycardia pacemakers and cardiacdefibrillators, have sense amplifier circuits for amplifying andfiltering electrogram signals picked up by electrodes placed in or onthe heart and which are coupled by suitable leads to the implantablecardiac rhythm management device. When a pacing pulse is delivered or anatural depolarization occurs in a heart chamber, the resultingpotential change appears at the input of the sensing channel for thatchamber. In order to prevent saturation of the sense amplifier in thissituation, the sensing channel can be blanked for a specified blankinginterval by disabling the sense amplifier when a pace is delivered orwhen a natural depolarization occurs. During the blanking interval, thedevice thus ignores all electrical activity that appears at the input ofthe sensing channel. Blanking intervals can be used not only to shieldthe sensing channel from pacing artifacts, but can also be used toprevent crosstalk between sensing channels where depolarizationoccurring in one cardiac chamber is interpreted as a depolarization inanother chamber. Such crosstalk occurs in the atrial sensing channelwhen a far-field sense resulting from a ventricular depolarization isinterpreted as an atrial sense. Accordingly, a cross-chamber blankinginterval for the atrial channel can be provided that is initiated afterdetection of a ventricular sense.

Because the cross-chamber blanking interval for the atrial sensingchannel starts with a ventricular event and lasts for a specified timethereafter, atrial depolarizations occurring shortly after ventriculardepolarizations at high ventricular rates may fail to be detected. Acardiac rhythm management device that implements a cross-chamberblanking interval for the atrial sensing channel may thus fail todistinguish an atrial tachyarrhythmia from a ventricular tachycardia. Adevice might then deliver ventricular anti-tachycardia pacing whenatrial anti-tachycardia pacing or an atrial defibrillation shock isactually the appropriate therapy.

In accordance with certain embodiments of the present invention, theatrial cross-chamber blanking interval is shortened when an atrial rateabove a specified limit rate is detected. In various embodiments, theblanking interval can be shortened by a predetermined amount or by anamount that varies with the ventricular rate.

FIGS. 4 and 5 illustrate cases where false atrial tachycardia detectioncould occur, as shown in these marker channel diagrams (illustrated aslines or graphs 181 and 182). The atrial pace, atrial refractory, andventricular pace events are simply indicated with AP, AR, and VP,respectively. In FIG. 4 an atrial-sensed event in a post ventricularatrial refractory period (PVARP 188) may be due either to far fieldR-waves (FFRWs), T-wave sensing, retrograde conduction, skeletal muscleactivity artifacts, or any other sense occurring during PVARP, or falseatrial sensing due to polarization after a pacing pulse. For heuristicpurposes and reference a PVAB period 189 (post ventricular atrialblanking period) is also shown within the PVARP 188 in FIG. 3. In asecond case (see FIG. 5), an atrial sense (AR) during the AtrioVentricular (AV) interval is shown. This may be due to ventricularfusion pacing, loss of atrial capture, junctional rhythm, or any otheratrial sense during the AV interval which can fool the tachy detectionalgorithm by suggesting that the true atrial interval (the intervalbetween the atrial pace events and not the interval between a pace eventand a sensed event) is very short.

Far field R-wave sensing may occur in cases other than an AP-AR-APrhythm. It is also possible to get a far field R-wave after a sinusrhythm, producing an AS-VP-AR marker channel series. While in general itmay be assumed that the marker channel diagram of FIG. 4 hasappropriately labeled marker signals, these may be incorrect. Forexample, a far field R-wave or other signal may appear to be somethingother than it seems. If that is the case, the marker channel generatorwill label it incorrectly, indicating that the pacemaker may respondincorrectly.

In other pulse generators, there may be no marker channel reference butthe device may nonetheless misinterpret signals. The marker channel isused in this description because it is much more easily read than stripcharts and because it indicates how the pacemaker is interpreting thesensed signals it is receiving from the heart and its environment.

FIG. 6 is a marker channel diagram 185, illustrating PVAB's (postventricular atrial blanking periods) 186 and also illustrating a blankedatrial refractory sense 188. Starting at the left, the AP-AS (blanked at188)—AR sequence is interpreted as an A-A interval measured from AP toAS, since the FFRW-type signal at 188 is ignored. Thus, in the case of along PVAB (Post Ventricular Atrial Blanking period) like PVAB 186, thenext marker channel atrial event is further out.

With reference to FIG. 7A, a marker channel diagram for sequentialpacing (illustrated as lines or graphs 201) of both ventricles incertain embodiments of the present invention is shown. It has been foundthat sequential pacing of the right and left ventricles instead ofsimultaneous pacing or single ventricle pacing as shown in FIGS. 4-6 canprovide improved hemodynamics. In sequential CRT pacing therapy, theventricle paces can be separated by as much as 80 ms. As shown in FIG.7, left ventricle pulse 200 is generally administered first after atrialevent 203 (a pacing pulse or a natural depolarization) as the leftventricle is the high pressure side of the heart. Anywhere from 10 ms to80 ms later a right ventricle pulse 202 is administered to the rightventricle. While this method of sequential CRT pacing has proven toimprove hemodynamics of the heart, it also introduces multiple (albeitoverlapping) blanking periods where typically only one had existed asshown in FIGS. 4-6.

After left ventricle pace 200, a first blanking period 204 beginstypically lasting approximately 100 ms. Then at a predetermined timeafter left ventricle pace 200, right ventricle pace 202 is administeredand second blanking period 206 begins typically lasting approximately100 ms.

This has the effect of extending the total blanking period by up to 80ms beyond first blanking period 204. Therefore, in effect, there is anadditional 80 ms where an atrial arrhythmia would not be detected. Forexample, atrial event 210 would not be detected within first blankingperiod 204 and second atrial event 212 would not be detected withinsecond blanking period 206.

FIG. 7B shows a marker channel diagram for simultaneous or singleventricle pacing (illustrated as lines or graphs 211) in certainembodiments of the present invention. Upon preliminary detection of anatrial arrhythmia microprocessor 224 mode switches to a confirmationmode B1 (FIG. 8), discussed in more detail below. In the confirmationmode, the left ventricle and right ventricle are simultaneously pulsedwith pulse 220 generally administered shortly after an atrial event 203(a pacing pulse or a natural depolarization). However, it is fullycontemplated that one ventricle is paced instead of both withoutdeparting from the spirit of the present disclosure. After ventriclepace 220, a first blanking period 204 begins typically lastingapproximately 100 ms. by shifting to sequential pacing, second blankingperiod 206 is eliminated thus reducing the total blanking period. Thiscan have the effect of increasing the ability to detect possible atrialarrhythmias. For example, atrial event 210 would still not be detectedwithin first blanking period 204, however, second atrial event 212 wouldbe detected now that second blanking period 206 is taken away, thusallowing for the detection of atrial even 212.

FIG. 7C shows a marker channel diagram for a blanking period during anatural depolarization event (illustrated as lines or graphs 221) incertain embodiments of the present invention. Upon preliminary detectionof an atrial arrhythmia, microprocessor 224 mode switches to aconfirmation mode B2 (FIG. 8), discussed in more detail below. In theconfirmation mode, the left ventricle and right ventricle are allowed todepolarize intrinsically with depolarization event 230. The ventriclesare only paced if no depolarization occurs after a ventricle toventricle delay from the previous R wave. After ventricle depolarization230, a shortened blanking period 224 begins typically lastingapproximately 30 ms. By shifting to natural or intrinsic depolarization,second blanking period 206 is eliminated and first blanking period 204is reduced, thus reducing the total blanking period. Therefore, atrialevents 210 and 212 are detected, allowing for the detection of an atrialarrhythmia.

With reference to FIG. 8, a flow chart diagram of an atrial arrhythmiadetection method according to certain embodiments of the presentinvention is shown. Implantable medical device 10 typically operates ina normal detection mode represented as state 300. In this operating modeIMD 10 operates in a DDD or DDDR pacing mode as is known in the art anddescribed in the incorporated references. The atrium is paced if nocontraction of the atrium occurs intrinsically after a period of delayfollowing the previous atrial contraction. In this pacing mode, theventricles are also paced if no contraction of the ventricles occursintrinsically. This ventricular pacing occurs after a predeterminedatrial-ventricular delay based upon the P wave. In normal detection mode300, the CRT mode is set to Sequential with VSR (ventricular senseresponse). That is, the ventricles are paced sequentially separated by apredetermined time. This time period can range from 10 ms to 80 msdepending on which time frame provides the best hemodynamics for theheart. The left ventricle is commonly paced first with the rightventricle paced afterwards. VSR pacing indicates that the ventricles arepaced upon sensing a ventricular event. Therefore, not only are theventricles sequentially paced after a period when no contraction occursintrinsically, but the ventricles are also sequentially paced upondetection of a ventricular event.

At state 302, microprocessor 224 will continually monitor the sensedevents from the atrium to determine whether any atrial arrhythmiasexist. There are many methods to detect atrial arrhythmias as discussedabove and with the incorporated references and as disclosed in U.S. Pat.No. 5,814,083 herein incorporated by reference in its entirety. In thepresent embodiment, the timing of atrial pacing, the AV delay and thevalue of the PVARP parameter in a dual chamber pacemaker are altered tointerrupt a pattern of persistent atrial blanking which results insensing every other atrial event. As stated above, however, extendedblanking periods 204 and 206 (see FIG. 7) can hinder atrial arrhythmiadetection. Nevertheless, microprocessor continues to monitor the sensedsignals from the atrium to determine if an arrhythmia is occurring. Inthe preliminary atrial arrhythmia detection at state 302, the thresholdfor determination of atrial arrhythmia is relatively low due to the lossof atrial data due to blanking periods 204 and 206. If no preliminaryatrial arrhythmia detection is made, microprocessor 224 returns to state300 and resumes normal operation. If a possible atrial arrhythmia isdetected, microprocessor 224 proceeds to state 304 where a determinationis made as to whether the clinician implanting IMD 10 set the device toproceed to a DDIR mode upon preliminary detection of an atrialarrhythmia.

If the mode switch is on, microprocessor 224 proceeds to state 306 wherea pacing mode change is made. If the mode switch is off, microprocessor224 proceeds to state 308 where the pacing mode remains the same.Additionally, the mode switch can be set to on with a delay period. Thelength of the delay period will often then dictate whether themicroprocessor proceeds to state 306 or 308 from state 304. If the delayis set longer than the threshold for preliminary detection ofAT/AF/atrial flutter at state 302 (i.e., state 304 requires a longerpresence of AT/AF/atrial flutter than state 302), the microprocessorwill still see a mode switch set in the “off” position when it passesfrom state 302 to 304. Accordingly, the microprocessor will switch tostate 308. Alternatively, if the delay is shorter than the threshold forpreliminary detection of AT/AF/atrial flutter at state 302 (i.e., state302 requires a longer presence of AT/AF/atrial flutter than state 304),the microprocessor will see a mode switch set in the “on” position whenit passes from state 302 to state 304. Accordingly, the microprocessorwill switch to state 306 under this scenario.

At state 308, IMD 10 switches to a confirmation mode before determiningif an atrial arrhythmia exists at state 310. In this confirmation modeB1, IMD continues to operate in a DDD or DDDR mode. That is, the atriumis paced if no contraction of the atrium occurs intrinsically after aperiod of delay following the previous atrial contraction. Moreover, asdiscussed above with reference to state 300, the ventricles are alsopaced if no contraction of the ventricles occurs intrinsically. Thisventricular pacing occurs after a predetermined atrial-ventricular (AV)delay based upon the P wave. In contrast to state 300, though, the CRTpacing is switched to the modified mode without VSR. In this modifiedmode, the ventricles are not paced upon sensing a ventricular event.Furthermore, the sequential bi-ventricular pacing of state 300 isreplaced with simultaneous bi-ventricular pacing (i.e., left and rightventricles paced simultaneously) or single-sided (left or rightventricle) pacing. By eliminating the sequential pacing therapy,blanking period 206 is eliminated, increasing the percentage of thecardiac cycle in which to detect an atrial arrhythmia.

At state 306 (confirmation mode B2), microprocessor 224 switches pacingmodes from a DDD or DDDR operation mode to a DDIR. In this“non-tracking” pacing mode, as is known in the art, the ventricles arepaced if no contraction of the ventricles occurs intrinsically after aperiod of delay following the previous ventricular contraction (VV delaybased upon the R wave). The atrium may also be paced if no contractionoccurs, but this is unlikely given that an atrial arrhythmia has beendetected (albeit only preliminarily at state 306). The CRT therapy modeis set to the same as that in state 308 modified with no VSR. Similar tostate 308, blanking period 206 is eliminated when removing thesequential pacing therapy, thereby lengthening the time period in whichto detect an atrial arrhythmia.

After switching to confirmation state 306 or 308, microprocessor 224will make a determination and confirm whether an atrial arrhythmiacontinues to exist at state 310. Unlike the preliminary determination atstate 302, the confirmation state of 310 has a higher threshold foratrial arrhythmia determination. This threshold could be similar thosedisclosed in the references incorporated above. For example, themicroprocessor may only require evidence of an atrial arrhythmia topersist for three ventricular cycles before a mode switch occurs—howeverthe episode may need to persist for up to 32 cycles before the atrialarrhythmia is considered sufficiently long to warrant consideration fortherapy. Such an example exists in the Medtronic Gem IIII AT Model 7276defibrillator, where the mode switch criteria is three ventricular beatswith evidence of atrial arrhythmia, however the criteria for therapywould be a minimum of 32 ventricular beats with this evidence present.Regardless, if an atrial arrhythmia is not confirmed at state 310,microprocessor 224 returns to state 300 and begins normal detectionmode. However, if an atrial arrhythmia is confirmed, microprocessor 224proceeds to a wait mode at state 312.

At state 312, the pacing mode is set at DDIR mode, like that discussedabove for state 306. CRT mode is returned to sequential bi-ventricularwith VSR, like that discussed above for state 300. While thisreintroduces blanking period 206, this is not a great concern since thearrhythmia has already been detected and therapy has already beenscheduled for some later time. That is, at state 312, microprocessor 224sets a time to administer an atrial therapy.

During the time period before the atrial therapy, microprocessor 224periodically advances to state 314 where it monitors the sensed atrialsignals to determine if the atrial arrhythmia is persisting. Since anatrial arrhythmia has already been detected, the threshold forpersisting arrhythmia is low. For comparison sake, the level ofarrhythmia for a preliminary detection of atrial arrhythmia is muchhigher at state 302 than it is at state 314. These algorithms typicallyemploy hysteresis to provide some stability when it is possible thatundersensing of the arrhythmia or brief pauses in the arrhythmia mayoccur. If the atrial arrhythmia has been found to have ceased at state314, microprocessor 224 returns to normal detection mode at state 300.If the atrial arrhythmia is persisting, but the time for the atrialtherapy has not been reached, microprocessor 224 returns to state 312continuing with the DDIR sequential ventricular pacing mode. If theatrial arrhythmia is persisting and it is time for the atrial therapy,microprocessor 224 proceeds to state 316 switching to an atrial therapymode.

In the therapy mode at state 316, the pacing mode is set at DDIR and theCRT mode at modified with no VSR. An appropriate atrial therapy is thenadministered such as a pacing therapy, cardioversion therapy, or adefibrillation therapy. If a defibrillation or cardioversion therapy isadministered, the therapy is timed from the ventricle pace or from thefirst of a sensed ventricle event. Once the atrial therapy isadministered, microprocessor 224 returns to the therapy at state 312 andthen confirms whether an atrial arrhythmia persists at state 314. If theatrial arrhythmia has ceased, microprocessor 224 returns to normaldetection mode at state 300. If the atrial arrhythmia is persisting, anew time for atrial therapy is set. If the time for the atrial therapyhas not been reached, microprocessor 224 returns to state 312 continuingwith the DDIR sequential ventricular pacing mode. If the atrialarrhythmia is persisting and it is time for the atrial therapy,microprocessor 224 proceeds to state 316 switching to an atrial therapymode.

After microprocessor 224 determines the presence of an atrial arrhythmiathat requires therapy, there are pacing and defibrillation/cardioversiontherapy considerations. Delivery of anti-tachy pacing, with occurs atrates similar to the tachycardia itself, should not be followed by CRTwith a 1:1 relationship. In addition, the separation of right ventricleand left ventricle paces might interfere with anti-tachy pacing deliverysince the IMD circuitry may require time between paces to allow for thecapacitor charging and sensing considerations. Thus, during ATPdelivery, CRT is modified as noted above to provide single site pacingonly or simultaneous right and left ventricle pacing.

For cardioversion/defibrillation, the presence of sequential right andleft ventricle pacing may interfere with determining the appropriate“safe” point within which to deliver an atrial therapy. Assuming thatIMD 10 will only deliver atrial shocks on ventricular cycle lengths of500 ms or more, if the right ventricle pace is followed 50 ms later by aleft ventricle pace, it is possible to begin the 500 ms window on eitherthe right ventricle or left ventricle pace. If the former, it may not besafe given the time of activation of the left ventricle. If on thelatter, it may be unable to synchronize given the large change in ratethese small interval adjustments produce at the rate range of interest.One solution as noted above is for the sequential pacing to be suspendedbefore and during cardioversion therapy to permit a more homogeneousdepolarization pattern in the ventricles that would provide a safershock delivery. At the time the shock is to be delivered, and optionallyfor some number of beats preceding the shock (such as during thecharging period) the device could use simultaneous or single-sitepacing.

Another improvement to delivery of atrial cardioversion would be theoption to synchronize the shock to the right or left ventricle sensedsignal. Current ICD's with anti-tachy therapy capability can only sensefrom the right side of the heart. With left ventricular sensing (andrapidly conducted atrial fibrillation activating the ventricles), thedevice could selectively synchronize to the left ventricle or rightventricle based on site of the earliest activation. This has theadvantage to provide the atrial shock simultaneous with the earliestventricular activation, understanding in these patients that it ispossible with ventricular disynchrony these activations occur atslightly different times.

Thus, embodiments of the DELIVERY OF CRT THERAPY DURING AT/AFTERMINATION are disclosed. The disclosed embodiments are presented forpurposes of illustration and not limitation, and the present inventionis limited only by the claims that follow.

1. A method for operating a cardiac rhythm management device,comprising: sensing atrial depolarizations through an implanted atrialelectrode; administering a sequential CRT pacing therapy in a sequentialCRT pacing mode to a left and right ventricle of a heart of a patientvia implanted ventricular electrodes in a sequential bi-ventricularfashion; switching from the sequential CRT pacing mode to a simultaneousCRT pacing mode; administering a simultaneous CRT pacing therapy in thesimultaneous CRT pacing mode to the left and right ventricle in asimultaneous bi-ventricular fashion; and analyzing the sensed atrialdepolarizations to detect the presence of an atrial arrhythmia.
 2. Themethod of claim 1, further including analyzing the sensed atrialdepolarizations while in the sequential CRT pacing mode to detect thepresence of atrial arrhythmia.
 3. The method of claim 1, furtherincluding sensing ventricular depolarizations of the left and the rightventricle.
 4. The method of claim 1, further including providing anatrial pacing therapy when no atrial depolarizations are sensed for apredetermined amount of time.
 5. The method of claim 1, furtherincluding switching from the simultaneous CRT pacing mode to thesequential CRT pacing mode when the presence of atrial arrhythmia is notdetected.
 6. The method of claim 1, further including switching from thesimultaneous CRT pacing mode to the sequential CRT pacing mode when thepresence of atrial arrhythmia is detected.
 7. A method for operating acardiac rhythm management device, comprising: administering a sequentialCRT pacing therapy in a sequential CRT pacing mode to a left and rightventricle of a heart of a patient via implanted ventricular electrodesin a sequential bi-ventricular fashion; switching from the sequentialCRT pacing mode to a modified CRT pacing mode; administering a modifiedCRT pacing therapy in the modified CRT pacing mode, the modified CRTpacing therapy being one of a simultaneous CRT pacing therapy and asingle-sided pacing therapy, the simultaneous CRT pacing therapy beingadministered to the left and right ventricle in a simultaneousbi-ventricular fashion, the single-sided CRT pacing therapy beingadministered to one of the left and right ventricles; and administeringan atrial electrical stimulation therapy via an implanted atrialelectrode to an atrium of the patient in the presence of an atrialarrhythmia.
 8. The method of claim 7, wherein the atrial electricalstimulation therapy includes at least one of anti-tachy pacing, atrialcardioversion, and atrial defibrillation.
 9. The method of claim 7,further including sensing atrial depolarizations.
 10. The method ofclaim 7, wherein switching from the sequential CRT pacing mode to themodified CRT pacing mode occurs before administering the atrialelectrical stimulation therapy.
 11. The method of claim 7, furtherincluding sensing ventricular depolarizations of the left and the rightventricle, and wherein the sequential CRT pacing therapy is applied uponsensing depolarization of the right or left ventricle.
 12. The method ofclaim 7, further including sensing ventricular depolarizations of theventricles, and wherein one of the sequential CRT pacing therapy and themodified pacing therapy is administered when no ventriculardepolarizations are sensed for a predetermined amount of time.
 13. Themethod of claim 7, further including switching from the modified CRTpacing mode to the sequential CRT pacing mode after administering theelectrical atrial stimulation therapy.
 14. A system for operating acardiac rhythm management device, comprising: means for sensing atrialdepolarizations through an implanted atrial electrode; means foradministering a sequential CRT pacing therapy in a sequential CRT pacingmode to a left and right ventricle of a heart of a patient via implantedventricular electrodes in a sequential bi-ventricular fashion; means forswitching from the sequential CRT pacing mode to a single-sided CRTpacing mode; means for administering a single-sided CRT pacing therapyin the single-sided CRT pacing mode to one of the left and rightventricle; and means for analyzing the sensed atrial depolarizations todetect the presence of an atrial arrhythmia.
 15. The system of claim 14,further including means for analyzing the sensed atrial depolarizationswhile in the sequential CRT pacing mode to detect the presence of atrialarrhythmia.
 16. The system of claim 15, wherein the analysis to detectthe presence of an atrial arrhythmia while in the sequential CRT pacingmode is a preliminary detection analysis.
 17. The system of claim 14,further including sensing ventricular depolarizations of the ventricles.18. The system of claim 14, further including providing an atrial pacingtherapy when no atrial depolarizations are sensed for a predeterminedamount of time.
 19. The system of claim 14, further including switchingfrom the single-sided CRT pacing mode to the sequential CRT pacing modewhen the presence of atrial arrhythmia is not detected.
 20. The systemof claim 14, further including switching from the single-sided CRTpacing mode to the sequential CRT pacing mode when the presence ofatrial arrhythmia is detected.